The objective of the proposed research is to elucidate in molecular terms the structural and metabolic interrelationships among the plasma lipoproteins and the heterogeneity that exists in each of the major class of lipoproteins. The studies involve characterization of lipoprotein species isolated from each of the major classes with respect to physical properties and content of specific lipids and apolipoproteins. The studies also involve further characterization of the protein moieties of the lipoproteins--apo B, Lp(a) polypeptide, the polymorphic variants of apo AI, apo E and two new threonine-poor apolipoproteins, and other apolipoproteins that have not yet been characterized. The results should better define the species of lipoproteins that contain a common apolipoprotein (S) but differ in density, and hence the interconversions responsible for their distribution among the different classes, as well as the molecular nature of lipoproteins of similar density.